Ensure cached filesystems' protocol is preserved (#1897)

Co-authored-by: Martin Durant <[email protected]>

Author: mraspaud

fsspec/implementations/cached.py

@@ -478,7 +478,7 @@ def __getattribute__(self, item):
         if item in ["transaction"]:
             # property
             return type(self).transaction.__get__(self)
-        if item in ["_cache", "transaction_type"]:
+        if item in {"_cache", "transaction_type", "protocol"}:
             # class attributes
             return getattr(type(self), item)
         if item == "__class__":

fsspec/implementations/tests/test_cached.py

@@ -1337,3 +1337,8 @@ def test_filecache_write(tmpdir, m):
 
     assert m.cat(fn) == data.encode()
     assert fs.cat(fn) == data.encode()
+
+
+def test_cache_protocol_is_preserved():
+    fs = fsspec.filesystem("filecache", target_protocol="file")
+    assert fs.protocol == "filecache"